Experiments and inelastic finite element analyses of plasma sprayed graded coatings under cyclic thermal shock

Elastic-plastic finite element models of plasma sprayed multi-layered graded coatings were developed to simulate the stress development during thermal shock cycling. In the models, the as-deposited stress and strain in an existing numerical "deposition model" [Z.H. Gan, Modeling of deposition and thermal shock of plasma spray coatings, Ph.D. Thesis, Nanyang Technological University, Singapore, 2002] is considered as the initial stress and strain conditions. In parallel, a heat transfer analysis was performed to calculate the temperature distribution in the specimen, which was input into the stress models as thermal load. The models were verified by in situ curvature and temperature measurement. Additionally, the performance of the coatings under thermal shock loading was experimentally determined using acoustic emission (AE) system, which is correlated to the stress and strain profiles during thermal shock predicted by the above models using a general purpose commercial FEM software ANSYS (ANSYS Inc., Southpointe, PA, USA). The samples' surfaces were examined by SEM prior to and after thermal shock cycling, indicating coating spallation, crack initiation and propagation. This article presents a method for assessing the influence of the number of graded layers on the residual and component stresses during cyclic thermal shock. (C) 2004 Elsevier B.V. All rights reserved.